1) What do people use to mount CM? 100% silicone? PL 700?
2) I'd like to mount the CM onto a Redgard-sealed plywood. Any thoughts on this idea? I understand Terry is a proponent of mounting CM directly onto Greenboard. That said, would either PL or silicone bond adequately to a Redgard surface?

If that scenario isn't described in the Redgard installation instructions, I think you'd be better off checking with Custom Building Products for your answer. I know thinset will stick to Redgard, but the mechanism is different than with an adhesive - the cement grows interlocking crystals into the flexible material as it cures, an adhesive won't.

Hi Footman...go to www.johnbridge.com
Its a site dedicated to all things tile and stone. Great advice from real tile pro's.
FWIW- What you are wanting to do is completely wrong. You will find out at John Bridge. Good luck.

Jim, are you familiar with Georgia-Pacific's DensShield? Spotted it at the hardware store. Looks like it might offer adequate moisture resistance and surface adhesion while reducing Redgard usage to joints only.
Thanks again for the input.

I have not used it personally, so I have no recommendations either way. Look at it this way, though, if you bond the seams properly, you have a solid panel, similar to any other solid surface like Corian, or Silestone...those are waterproof in their own right, so it shouldn't really matter what's behind it. What are you using to seam the panels together? If it is their proprietary material, it should make the sheets into what effectively is one solid sheet.

I purchase, update, and maintain small income properties that are in disrepair. So it is my property, not my home. Definitely interested in doing this job right.

Last time I used CM I had the fabricator do the install. He used PL as adhesive. He did a terrible job on the installation (wrecked my tiles, ceiling, cut mixer valve hole in wrong place of the CM....) So I am less inclined to trust his process. That said I'm told that PL is a valid adhesive as is 100% silicone for installing CM. I've also heard that PL becomes visible through the CM, especially if you go with a white CM. (Can't see it on the most recent install mind you)

Anyhow, you're right in suggesting that I need to nail down exactly what adhesive is best for fastening CM. I'm leaning towards silicone. I'm also leaning away from Redgard. Seems like it's only meant to accept mortar.

Other option I'm considering is 1) 1/4" ply, 2) Redgard coat, then 3) HardiBoard backer. Risk here is that any cracks in the CM seams will allow moisture into the Hardiboard. Still, given the nature of CM and the limited number of seams, and the fact that silicone will be in those seams, I'm comfortable with this plan....so far....

Still waiting to hear from CPB on Redgard limitations visavis adhesives.

Any adhesive that has any oil in it can stain some of those composite panels, and since many of them are somewhat translucent, an uneven coat of anything, especially dark in color, can show through in some lighting. While lots of things may cause it to stick and stay there, not all are good choices. I think I'd rather use the epoxy or whatever material is designed to bond the panels into one, homogenous water-tight assembly, rather than using silicon. The 'right' stuff can be sanded and polished into an invisible seam, the silicon may last a long time, but is harder to get nice and smooth, and some silicons exude some oil when the cure so be careful of the type.

We've installed a number of CM and solid surface (corian et al) wall coverings in showers. Most manufacturers have suggested drywall substrates and clear silicone adhesive - a few suggested liquid nails and included some in their install kits. Be careful with using adhesives that could react with the CM/solid surfacing material - this is why I asked what the manufacturer suggests.

As the CM/solid surfacing is waterproof, all we've done to make the install completely waterproof is to flash the corners behind the solid surfacing and make sure it all overlaps the receptor flange. If possible, it's nice to set both flashing and solid surfacing into sealant over the flange AND set the solid surfacing into sealant over the flashing. Regardless, after flashing the corners, and setting the wall panels, we finish with silicone in the corners between panels and at the receptor. For flashing, we've used any number of things from rips of shower pan liner to aluminum to strips of Kerdi.

No need for Redgard, backer board or any of the rest...

I know this works well as we have a few installs 15-20 years old that look like new.

Heard back from CBP. They say if you want to apply onto Redgard any adhesive other than thin set, to do the following: Apply a skim coat of Speed Finish Patching & Finishing Compound onto the RG then apply adhesive onto skim coat.